The present application claims priority to Japanese Application No. P10-218364 filed Jul. 31, 1998, which application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
This invention relates to an anti-reflection film and a cathode ray tube. More particularly, it relates to an anti-reflection film that is able to improve tightness of adhesion of the thin optical film to a substrate, and to achieve anti-reflection effects over a wide wavelength range, and a cathode ray tube employing this anti-reflection film.
2. Description of the Related Art
Up to now, an anti-reflection film has been used in the optical and in electro-optical field where it is desirable or necessary to decrease the refractive index on an optical interface between air and glass. Specifically, the field of usage for the anti-reflection film covers a wide field encompassing a camera lens, a platen for a copying machine, cover glass for equipments, a panel for a cathode ray tube (CDT) and other display devices.
This anti-reflection film may be enumerated by a film configured as shown for example in FIG. 1. This film is comprised of a resin substrate 101, on a major surface 101a of which are sequentially formed a first layer 102 of SiOx, where x less than 2, having a thickness of 10 nm, a second layer 103 of ITO, having a thickness of 20 nm, a third layer of SiO2, having a thickness of 25 nm, a fourth layer 105 of ITO, having a thickness of 60 nm, and a fifth layer 106 of SiO2, having a thickness of 100 nm.
This anti-reflection film has, however, an inconvenience that it has a multi-layered structure with as many as five layers, and a thicker total film thickness of 215 nm, so that it is difficult and pains-taking to manufacture, while being poor in productivity and high in production cost.
Thus, a demand is raised for an anti-reflection film having a smaller number of layers. If the number of layers is smaller, the number of layering steps is decreased to facilitate the production and improve the productivity as well as to lower the production cost.
In order to meet this demand, there has been proposed an anti-reflection film of a dual structure having on a substrate a thin film mainly composed of TiN and an SiO2 thin film of lower refractive index, as a second optical film, as disclosed in Japanese Laying-Open Patent H-9-156964, Japanese Laying-Open Patent H-9-165231 or in Japanese Laying-Open Patent H-9-73001.
However, this anti-reflection film, while having acceptable anti-reflection characteristics, is not optimum in adhesion between the substrate and the thin film, mainly composed of TiN, such that the film is susceptible to exfoliation and difficult to use practically.
It is therefore an object of the present invention to provide a practically useful anti-reflection film which has a small number of layers and high productivity and which is easy and simple to manufacture while being low in production cost and superior in anti-reflection characteristics.
It is another object of the present invention to provide anti-reflection sheet and a cathode ray tube employing this anti-reflection film.
According to the present invention, there is provided an anti-reflection film wherein an adhesive layer is formed on a major surface of a resin substrate, a first optical thin film containing one or more of titanium nitride, hafnium nitride or zirconium nitride is formed on the adhesive layer, and wherein a second optical thin film having a refractive index of 1.35 to 1.7 is formed on the first optical thin film.
Preferably, the adhesive layer is represented by the chemical formula of SiOx, where x less than 2. The adhesive layer may be formed of a compound represented by the chemical formula of SiNx, where x less than 4/3, or by the chemical formula of SiOxNy, where x less than 2 and y less than 4/3.
If, when the adhesive is formed of a compound having the chemical formula SiOx, where x less than 2, sufficient bonding strength between the resin substrate and the first optical thin film cannot be developed. If the value of x is too small, silicon is metallized to increase undesirably the optical absorption characteristics to impair the anti-reflection characteristics.
In the anti-reflection film of the present invention, the adhesive layer may predominantly be composed of Ti.
In the anti-reflection film of the present invention, the physical film thickness of the adhesive layer is preferably not larger than 10 nm and more preferably 1 to 7 nm. If the physical film thickness of the adhesive layer is thicker than 10 nm, optical absorption characteristics of the adhesive layer become excessive to impair undesirably the anti-reflection characteristics. If the physical film thickness is thinner than 1 nm, sufficient bonding strength between the resin substrate and the first optical thin film undesirably cannot be developed.
In the anti-reflection film of the present invention, the physical film thickness of the first optical thin film is preferably 5 to 25 nm. If the physical film thickness is outside this range, sufficient anti-reflection characteristics cannot be achieved.
In the anti-reflection film of the present invention, it is desirable for the first optical thin film to contain mainly titanium nitride and for titanium nitride to be doped with metal. This metal may be exemplified by tungsten and gold.
If the first optical thin film mainly contains titanium nitride, the first optical thin film desirably is electrically conductive.
In the anti-reflection film of the present invention, the first optical thin film preferably is composed of SiO2, while the physical film thickness of the second optical thin film preferably is 60 to 110 nm. If the second optical thin film composed of SiO2 is outside the above range, sufficient anti-reflection characteristics cannot be obtained.
In the anti-reflection film of the present invention, a hard coating layer preferably is formed on the surface of the resin substrate facing the adhesive layer, while an adhesive layer preferably is formed on the hard coating layer.
The above-described anti-reflection film of the present invention may be arranged on the face plate surface of a display portion to constitute the cathode ray tube.
In the cathode ray tube of the present invention, it is preferred that the first optical thin film of the anti-reflection film predominantly contains titanium nitride, this first optical thin film being electrically conductive and grounded.
In the anti-reflection film of the present invention, since the adhesive layer is formed on the major surface of the resin substrate, the first optical thin film containing one or more of titanium nitride, hafnium and zirconium nitride is formed on the adhesive layer, and the second optical thin film having the refractive index of 1.35 to 1.7 is formed on the first optical thin film, the number of layers is small to facilitate and simplify the manufacturing process to reduce the cost.
In the anti-reflection film of the present invention, since the adhesive layer is interposed between the resin substrate and the first optical thin film containing one or more of titanium nitride, hafnium and zirconium nitride, the first optical thin film is not liable to be detached from the resin substrate to assure good practically suitable anti-reflection characteristics.
Therefore, in the cathode ray tube of the present invention, in which the anti-reflection film of the present invention is arranged on the surface of the face plate of the display portion thereof, the anti-reflection characteristics are similarly good and practically suitable.
Also, in the anti-reflection film of the present invention, if the adhesive layer is formed of a compound represented by the chemical formula of SiOx, where x less than 2, the first optical thin film is less liable to be detached from the resin substrate.
If, in the anti-reflection film of the present invention, the first optical thin film mainly is composed of titanium nitride, and the first optical thin film is electrically conductive, the first optical thin film may be used as an electrically conductive film in place of the ITO layer used as an electrically conductive film in the conventional anti-reflection film.
Also, if, in the anti-reflection film of the present invention, the first optical thin film is formed of titanium nitride, having strong absorption characteristics, and the anti-reflection film is arranged on the face plate surface of the cathode ray tube, the image displayed on the cathode ray tube can be improved in contrast.
In the anti-reflection film of the present invention, in which an adhesive layer is formed on a major surface of a resin substrate, a first optical thin film containing one or more of titanium nitride, hafnium nitride or zirconium nitride is formed on the adhesive layer and in which a second optical thin film having a refractive index of 1.35 to 1.7 is formed on the first optical thin film, the number of layers is small, so that the manufacture may be facilitated and simplified to reduce the manufacturing cost to improve the productivity.
In the anti-reflection film of the present invention, in which an adhesive layer is interposed between the resin substrate and the first optical thin film containing one or more of titanium nitride, hafnium nitride or zirconium nitride, the first optical thin film is not liable to be detached from the resin substrate to assure good and practically acceptable anti-reflection characteristics.
In the cathode ray tube in which the anti-reflection film of the present invention is arranged on the face plate surface side of a cathode ray tube, the anti-reflection characteristics are similarly good and practically acceptable.
If, in the anti-reflection film of the present invention, the adhesive layer is formed of a compound represented by the chemical formula SiOx, where x less than 2, it is possible to suppress detachment of the first optical thin film from the resin substrate 3 further.
If, in the anti-reflection film of the present invention, the first optical thin film is mainly composed of titanium nitride, and the first optical thin film is electrically conductive, the first optical thin film may be used as an electrically conductive film in place of the ITO layer used as the electrically conductive film in the conventional anti-reflection film to render it unnecessary to provide an electrically conductive film to improve the productivity.
Also, in the anti-reflection film of the present invention, if the first optical thin film is formed of titanium nitride, having strong absorption characteristics, and the anti-reflection film is provided on the face plate side of the cathode ray tube as in the present invention, the image displayed on the cathode ray tube may be improved in contrast.